1 . Field of the Invention
The present invention relates to a piezoelectric element used in actuators and the like for injectors that are used for applicators for adhesive, coating agents, or the like, inkjet devices, fuel injection systems for internal combustion engines, and the like and are capable of accurate, high-speed discharge.
2 . Description of the Related Art
Piezoelectric elements are widely used in various industrial fields and various elements have been conventionally developed to the respective applications. As a conventional technology related to a piezoelectric element that can achieve a relatively large displacement (stroke), the following piezoelectric element is disclosed in JP-A-H4-167580: a piezoelectric element obtained by stacking multiple subunits of such an inner electrode structure that a piezoelectric inactive portion is provided.
There is also the piezoelectric element described in JP-A-2000-150977. This is a piezoelectric element obtained by joining together multiple chip blocks, formed by laminating multiple piezoelectric element chips each having a piezoelectric material and an inner electrode, with a joining layer in-between. In this piezoelectric element, the inner electrode is so formed as to cover a cross section of the piezoelectric material perpendicular to the direction of lamination and an electrical insulation layer is provided at an end of the inner electrode exposed from a side face of the piezoelectric element.
In recent years, however, materials not only satisfy the large discharge displacement but also impose less load in terms of environment have been required and a nonleaded material is sought for in place of lead zirconate titanate (PZT) that has been conventionally used as a piezoelectric material.
As a nonleaded piezoelectric material, for example, BaTi2O5 described in JP-A-2004-231500 is considered to be promising. However, it turned out that BaTi2O5 solely does not deliver sufficient piezoelectric performance and cannot achieve a large displacement.
The present inventors found that the following took place in a piezoelectric element having a piezoelectric material containing BaTi2O5 as the principal constituent material and a voltage application electrode. That is platinum and silver-palladium conventionally used for electrodes are inferior in lattice matching with BaTi2O5 as a piezoelectric material, and sufficient piezoelectric performance or reliability cannot be obtained because the atomic arrangement is disturbed in the interface between them. In these piezoelectric elements, a sufficient displacement cannot be obtained in the piezoelectric material when voltage is applied and the displacement is reduced with time.
It is an object of the invention to provide a novel piezoelectric element that is high in piezoelectric performance, and makes it possible to obtain a sufficient displacement and is reliable.